Irrigation is needed in many arid areas for supplying water to architectural vegetation. Greenery is often planted around homes, commercial buildings and apartment developments to provide an attractive outdoor appearance for them. In order to minimize the manual labor of such irrigation and to avoid loss of plants when irrigation is forgotten, clocks are often used to control electrically actuated valves which supply water to the irrigation system. Such clocks have been developed to a point where one or more days of the week can be selected for sprinkling. Furthermore, the time of day and duration of sprinkling can also be selected. Such clocks sometimes have a plurality of terminals which can be connected to different water control valves for the control thereof Such terminals are often referred to as stations. The clock usually sequentially energizes the stations, and the clock can be adjusted so that each station has its own individual adjustment of on time. In this way, irrigation of a number of different areas, each served by a station and a sprinkler valve, can be employed to deliver water to these areas in accordance with the program determined by the clock and independent of ground moisture. It would be desirable to conserve water by limiting the delivery of irrigation water when the ground moisture is adequate.
Irrigation systems are well-known for applying water to turf areas for maintaining the turf or vegetation growing there. Such systems include sprinklers distributed over the area, valves for controlling the flow of pressurized water to the sprinklers from underground water supply pipes, and an irrigation controller for operating the valves in accordance with a desired irrigation cycle stored in the controller. The controller often includes solid state logic means which allows the user to input and store practically any desired irrigation cycle.
Many known irrigation controllers operate automatically as time elapses to turn the sprinkler valves on and off at designated intervals without taking actual environmental conditions, i.e. actual soil moisture, into account. However, this is wasteful and unduly expensive as it uses water which may not be needed. In some cases, the irrigation controller includes a rain switch to stop an irrigation cycle when it is raining. While useful, this is not an exact measure of soil moisture and can potentially stop an irrigation cycle that may be needed despite the rain.
Interest has grown recently in soil moisture sensing technology in which the soil moisture level is measured directly and is used to control the irrigation process. Various types of soil moisture sensors have been proposed, including some which interface directly with an irrigation controller or valve to apply a control function. Such sensors usually provide a soil moisture reading when an input voltage is applied to them.
Many shrubs and trees have extensive root systems which reach deep into the soil profile, typically one to two feet. Most turf and ground cover have relatively shallow roots and require more frequent application of water to replace evapotranspiration because the soil reservoir available to their root system is relatively small. Existing practice with typical timer control systems is to provide a dual program control which enables two separate groups of valves to be timed independently for a number of days between irrigations and to water for durations which are independent of each other. The problem with that type of control is that it is quite arbitrary and independent of a situation which varies from day to day as the weather changes and it has no tangible relationship with plant water use.
Some systems use Envirotranspiration (ET). ET based systems are inaccurate and inefficient due to the simple fact that they rely on information collected above ground to theorize possible soil conditions to make watering decisions to an over-all-area. ET is only valid in the propagation one species of plan life in one given set of conditions thus on multiple species of plant life in multiple conditions, elevations and soil types, the ET equation is invalid for landscape irrigation. While many "rain check" devices will stop irrigation during and after a downpour, these devices have no way of compensating for evaporation or lack thereof over the 72 hour period immediately following rain and are easily fooled.
Prior art irrigation systems typically comprise multiple piping branches, with each branch being controlled by separate solenoid valves. Each solenoid valve is connected to a master irrigation controller and controls the flow of water from an entire piping branch. The master irrigation controller has a clock which is set to operate the solenoid valves over preselected time intervals, which are usually spaced apart by several days. Each of the piping branches extends in parallel to the other piping branches for distributing water to a defined irrigation zone, with an irrigation zone being herein defined as a region of soil which is serviced by a single piping branch. The piping branches include multiple spray heads having spray patterns which preferably overlap with the spray patterns of adjacent spray heads.
A problem with prior art irrigation systems arises since single irrigation zones will often include different types of vegetation, some of which require more frequent irrigation than other types disposed along the same piping branch. For example, a single piping branch may service an irrigation zone which includes a region of lawn grass, a region of flower beds, and both high spots, from which water will quickly run off, and low spots, where water will pool. Also, different soil types may be encountered within an irrigation zone of a consistent vegetation type. The relative amounts of water to be delivered to separate ones of the regions within a zone may differ depending upon environmental conditions, such that resizing of spray head capacities and spray patterns does not consistently alleviate this problem. Additionally, it is cost prohibitive to reroute piping branches and change spray heads when changes are made to the placement and types of vegetation found in regions services by a particular irrigation system.
Another problem with prior art irrigation system arises in irrigation systems used for preventing damage to building foundations. Where soils having high clay contents are encountered, the soil beneath building foundations are irrigated to assure consistent moisture levels over time. Prior art foundation irrigation systems are typically operated over preselected time intervals, with the irrigation system master clock controlling actuation of a solenoid valve which controls the flow of water from an entire foundation irrigation piping branch. Variations in elevation and the content of soils which extend beneath a foundation often result in varying irrigation requirements. Normally occurring changes in environmental conditions will also cause variations in moisture requirements over time. Irrigation systems which utilize a only master clock and single solenoid control valves to control piping branches, with only one control valve per piping branch to control the delivery of water to a single zone, cannot compensate for such variations.
Some prior art irrigation systems include a moisture sensor to control operation of the irrigation system in conjunction with the master clock. Prior art moisture sensors typically have two probes which extend vertically in the soil, spaced apart by a section in which moisture collects to complete a circuit between the two probes. Such prior art moisture sensors detect an averaged moisture level across a vertical distance within the soil. However, the root systems of a particular type of vegetation will usually extend downward to a particular depth within the soil. Prior art irrigation systems are not able to detect a when a preselected level of moisture content occurs at a particular depth within a soil, such that the depth of the moisture level relative to the root system of vegetation may be determined.